1.  2005 Pearson Education, Inc. All rights reserved. 1 1 1 Introduction

2.  2005 Pearson Education, Inc. All rights reserved. 2 History of Java Java – Originally for intelligent consumer-electronic devices – Then used for creating Web pages with dynamic content – Now also used to: Develop large-scale enterprise applications Enhance WWW server functionality Provide applications for consumer devices (cell phones, etc.)

3.  2005 Pearson Education, Inc. All rights reserved. 3 Java Class Libraries Classes – Include methods that perform tasks Return information after task completion – Used to build Java programs Java provides class libraries – Known as Java APIs (Application Programming Interfaces)

4.  2005 Pearson Education, Inc. All rights reserved. 4 When programming in Java, you will typically use the following building blocks: Classes and methods from class libraries, classes and methods you create yourself and classes and methods that others create and make available to you.

5.  2005 Pearson Education, Inc. All rights reserved. 5 Typical Java Development Environment Java programs normally undergo five phases – Edit Programmer writes program (and stores program on disk) – Compile Compiler creates bytecodes from program – Load Class loader stores bytecodes in memory – Execute JVM translates bytecodes into machine language

6.  2005 Pearson Education, Inc. All rights reserved. 6 OBJECTIVES In this chapter you will learn: To write simple Java applications. To use input and output statements. Java’s primitive types. Basic memory concepts. To use arithmetic operators. The precedence of arithmetic operators. To write decision-making statements. To use relational and equality operators.

7.  2005 Pearson Education, Inc. All rights reserved. 7 Outline Welcome1.java

8.  2005 Pearson Education, Inc. All rights reserved. 8 First Program in Java: Printing a Line of Text (Cont.) – Comments start with: // Comments ignored during program execution Document and describe code Provides code readability – Traditional comments: /*... */ /* This is a traditional comment. It can be split over many lines */ – Another line of comments 1 // Fig. 2.1: Welcome1.java 2 // Text-printing program.

9.  2005 Pearson Education, Inc. All rights reserved. 9 First Program in Java: Printing a Line of Text (Cont.) – Begins class declaration for class Welcome1 Every Java program has at least one user-defined class Keyword: words reserved for use by Java – class keyword followed by class name Naming classes: capitalize every word – SampleClassName 4 public class Welcome1

10.  2005 Pearson Education, Inc. All rights reserved. 10 First Program in Java: Printing a Line of Text (Cont.) – Java identifier Series of characters consisting of letters, digits, underscores ( _ ) and dollar signs ( $ ) Does not begin with a digit, has no spaces Examples: Welcome1, $value, _value, button7 – 7button is invalid Java is case sensitive (capitalization matters) – a1 and A1 are different 4 public class Welcome1

11.  2005 Pearson Education, Inc. All rights reserved. 11 First Program in Java: Printing a Line of Text (Cont.) – Saving files File name must be class name with.java extension Welcome1.java – Left brace { Begins body of every class Right brace ends declarations (line 13) 4 public class Welcome1 5 {

12.  2005 Pearson Education, Inc. All rights reserved. 12 Common Programming Error It is an error not to end a file name with the.java extension for a file containing a class declaration. If that extension is missing, the Java compiler will not be able to compile the class declaration.

13.  2005 Pearson Education, Inc. All rights reserved. 13 First Program in Java: Printing a Line of Text (Cont.) – Part of every Java application Applications begin executing at main – Parentheses indicate main is a method (Ch. 3 and 6) – Java applications contain one or more methods Exactly one method must be called main – Methods can perform tasks and return information void means main returns no information – Left brace begins body of method declaration Ended by right brace } (line 11) 7 public static void main( String args[] ) 8 {

14.  2005 Pearson Education, Inc. All rights reserved. 14 First Program in Java: Printing a Line of Text (Cont.) – Instructs computer to perform an action Prints string of characters – String - series characters inside double quotes White-spaces in strings are not ignored by compiler – System.out Standard output object Print to command window (i.e., MS-DOS prompt) – Method System.out.println Displays line of text – This line known as a statement Statements must end with semicolon ; 9 System.out.println( "Welcome to Java Programming!" );

15.  2005 Pearson Education, Inc. All rights reserved. 15 Common Programming Error Omitting the semicolon at the end of a statement is a syntax error.

16.  2005 Pearson Education, Inc. All rights reserved. 16 First Program in Java: Printing a Line of Text (Cont.) – Ends method declaration – Ends class declaration 11 } // end method main 13 } // end class Welcome1

17.  2005 Pearson Education, Inc. All rights reserved. 17 Modifying Our First Java Program (Cont.) Modifying programs -Displays “Welcome to ” with cursor remaining on printed line -Displays “Java Programming! ” on same line with cursor on next line System.out.print( "Welcome to " ); System.out.println( "Java Programming!" );

18.  2005 Pearson Education, Inc. All rights reserved. 18 Some common escape sequences.

19.  2005 Pearson Education, Inc. All rights reserved. 19 Outline

20.  2005 Pearson Education, Inc. All rights reserved. 20 Displaying Text with printf System.out.printf – Displays formatted data – Format specifier %s – placeholder for a string Welcome to Java Programming! System.out.printf ("%s\n%s\n", "Welcome to","Java Programming!" );

21.  2005 Pearson Education, Inc. All rights reserved. 21 Another Java Application: Adding Integers Upcoming program – Use Scanner to read two integers from user – Use printf to display sum of the two values – Use packages

22.  2005 Pearson Education, Inc. All rights reserved. 22 Outline

23.  2005 Pearson Education, Inc. All rights reserved. 23 Outline

24.  2005 Pearson Education, Inc. All rights reserved. 24 Another Java Application: Adding Integers (Cont.) – import declarations Used by compiler to identify and locate classes used in Java programs Tells compiler to load class Scanner from java.util package – Begins public class Addition 3import java.util.Scanner; // program uses class Scanner 5 public class Addition 6 {

25.  2005 Pearson Education, Inc. All rights reserved. 25 Common Programming Error All import declarations must appear before the first class declaration in the file. Placing an import declaration inside a class declaration’s body or after a class declaration is a syntax error.

26.  2005 Pearson Education, Inc. All rights reserved. 26 Error-Prevention Tip Forgetting to include an import declaration for a class used in your program typically results in a compilation error containing a message such as “ cannot resolve symbol. ”

27.  2005 Pearson Education, Inc. All rights reserved. 27 Another Java Application: Adding Integers (Cont.) – Variable Declaration Statement Input is of type Scanner – Enables a program to read data for use System.in Standard input object Declarations end with semicolons ; 10 //create Scanner to obtain input from command window 11 Scanner input = new Scanner( System.in );

28.  2005 Pearson Education, Inc. All rights reserved. 28 Another Java Application: Adding Integers (Cont.) – Declare variable number1, number2 and sum of type int int holds integer values (whole numbers): i.e., 0, -4, 97 Types float and double can hold decimal numbers Type char can hold a single character: i.e., x, $, \n, 7 – Can declare multiple variables of the same type in one declaration 13 int number1; // first number to add 14 int number2; // second number to add 15 int sum; // second number to add int number1,number2,sum;

29.  2005 Pearson Education, Inc. All rights reserved. 29 Another Java Application: Adding Integers (Cont.) – Message called a prompt - directs user to perform an action – Result of call to nextInt given to number1 using assignment operator = Assignment statement – = binary operator - takes two operands Expression on right evaluated and assigned to variable on left Read as: number1 gets the value of input.nextInt() 17 System.out.print( "Enter first integer:" ); 18 number1 = input.nextInt(); // read first number from user

30.  2005 Pearson Education, Inc. All rights reserved. 30 Software Engineering Observation By default, package java.lang is imported in every Java program; thus, java.lang is the only package in the Java API that does not require an import declaration.

31.  2005 Pearson Education, Inc. All rights reserved. 31 Another Java Application: Adding Integers (Cont.) Prompts the user to input the second integer Assign variable number2 to second integer input -Assignment statement Calculates sum of number1 and number2 (right hand side) Uses assignment operator = to assign result to variable sum Read as: sum gets the value of number1 + number2 number1 and number2 are operands 20 System.out.print( "Enter second integer: " ); 21 number2 = input.nextInt(); 23 sum = number1 + number2;

32.  2005 Pearson Education, Inc. All rights reserved. 32 Another Java Application: Adding Integers (Cont.) – Use System.out.printf to display results – Format specifier %d Placeholder for an int value 25 System.out.printf( "Sum is %d\n: ", sum ); System.out.printf( "Sum is %d\n: ",( number1 + number2 ) );

33.  2005 Pearson Education, Inc. All rights reserved. 33 Memory Concepts Variables – Every variable has a name, a type, a size and a value Name corresponds to location in memory – When new value is placed into a variable, replaces (and destroys) previous value – Reading variables from memory does not change them

34.  2005 Pearson Education, Inc. All rights reserved. 34 Memory location showing the name and value of variable number1.

35.  2005 Pearson Education, Inc. All rights reserved. 35 Memory locations after storing values for number1 and number2.

36.  2005 Pearson Education, Inc. All rights reserved. 36 Memory locations after calculating and storing the sum of number1 and number2.

37.  2005 Pearson Education, Inc. All rights reserved. 37 Arithmetic operators.

38.  2005 Pearson Education, Inc. All rights reserved. 38 Equality and relational operators.

39.  2005 Pearson Education, Inc. All rights reserved. 39 Precedence and associatively of operations discussed.